In less than a month, AliveCor plans to release its KardiaMobile 6L, which will provide 6 ECG leads using a smartphone-based mobile ECG system that is similar to the Kardia single-lead system.

AliveCor's website proclaims, "This is your heart x 6."

My first impressions are that this is a remarkable step forward in the technology of personal ECG monitoring. I'm not sure if I would call it "your heart x 6," but I feel the ability to view six high-quality leads compared to one is definitely going to add to the diagnostic capabilities of the Kardia device.

Kardia 6L Setup and Hardware

The 6L is similar in design and function to the single-lead device.

Once paired to the Kardia smartphone app (available for iOS or Android smartphones for free) it communicates with the smartphone using Bluetooth to create ECG tracings.

Like the single-lead Kardia, the 6L has two sensors on top for left and right hand contact. But in addition, there is a third on the bottom which can be put on a left knee or ankle.

If one uses the single-lead Kardia device in the traditional manner (left hand and right hand on the sensors), one is recording ECG lead I. However, if you put your right hand on the right sensor and touch the left sensor to your left leg, you are now recording ECG lead II and if to the right leg, ECG lead III. I describe this in detail here.

The combination of these sensors and contact points yield the six classic frontal leads of a full 12-lead ECG: leads I, II, III, aVL, aVR, and aVF. This is accomplished, AliveCor points out, "without messy gels and wires."

I found that using the device was simple and straight-forward and we were able to get high-quality tracings with minimal difficulty within a minute of starting the process in all the patients we tried it on.

My feeling is that by automatically including the leg (and leads II and III), the 6L will intrinsically provide high voltage leads for review and analysis, thereby improving the ability to accurately classify rhythm.

Totally unrelated to the 6L discussion, one can also record precordial ECG leads by putting the device on the chest and thus theoretically completing the full 12 leads of the standard ECG.

The Diagnostic Power of Six Leads

Below is a tracing on a patient with known atrial fibrillation. The algorithm correctly diagnoses it. With six different views of the electrical activity of the atrium, I (and the Kardia algorithm) have a better chance of determining if P waves are present, thereby presumably increasing the accuracy of rhythm determination.

Depending on the electrical vector of the left and right atria, the best lead to visualize P waves varies from patient to patient. Thus, having six to choose from should improve our ability to differentiate sinus rhythm from afib.

In the example below, the Kardia 6L very accurately registered the left axis deviation and left anterior fascicular block that we also noted on this patient's 12 lead ECG. This 6L capability, determining the axis of the heart in the frontal plane, will further add to the useful information Kardia provides.

For a good summary of axis determination and what abnormal axes tell us, see here.

The History of ECG Leads

When I began my cardiology training the 12-lead ECG was standard, but it has not always been that way. I took this timeline figure from a nice review of the history of the ECG:

Willem Einthoven's first three-lead EKG in 1901 was enormous. This photo from that paper shows a string galvanometer electrocardiograph with the patient's extremities in the cylindrical electrodes filled with electrolyte solution.

It is mind-boggling to consider that we can now record six ECG leads with a smartphone and a device the size of a stick of gum.

For the first 30 years of the ECG era, cardiologists only had three ECG leads to provide information on cardiac pathology. Here's a figure from a state of the art paper in 1929 on "coronary thrombosis" (which we now term a myocardial infarction) showing changes diagnostic of an "attack" and subsequent atrial fibrillation.

In the 1930s, the six precordial leads were developed providing more information on electrical activity in the horizontal axis of the heart. The development of the augmented leads (aVR, aVL, aVF) in 1942 filled in the gaps of the frontal plane. The combination of all of these 12 leads was sanctified by the American Heart Association in 1954.

I'll write a more detailed analysis of the Kardia 6L after spending more time using it in patient care.

Relative accuracy of the 6L versus the single-lead Kardia for afib determination, which at this point would be the major reason for current Kardia users to upgrade

Utility of the 6L for determination of cardiac axis and electrical intervals in comparison to the standard 12-lead ECG, especially in patients on anti-arrhythmic drugs

For now, this latest output from the meticulous and thoughtful folks at AliveCor has knocked my socks off!

Please also note that I have no financial or consulting ties to AliveCor. I'm just a big fan of their products.

Anthony Pearson, MD, is a private practice noninvasive cardiologist and medical director of echocardiography at St. Luke's Hospital in St. Louis. He blogs on nutrition, cardiac testing, quackery, and other things worthy of skepticism at The Skeptical Cardiologist, where a version of this post first appeared.

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